A method for clarifying gas streams is known from WO 2008/010717. In this method, gas leaving a biomass reactor is subjected to a hydrocarbon oil flow. Excess oil is recirculated and is used after filtration for contact with the gas from the reactor. Additional oil is received from a downstream separation device into which the gas is entered.
WO 03/018723 discloses a so-called OLGA system for gasifying biomass. The gas which results from gasification is subjected to a two-step cleaning treatment for removing tars. In a first step the gas is condensed in a first cleaning fluid which is a hydrocarbon oil. Saturation can take place for example by spraying oil in the gas stream. In a second stage oil is used for absorption of the remaining tars in an absorption column. After use the oil with tars is discharged to a separator wherein the heavy fractions are returned to the biomass gasifier and the lighter fractions are further used as oil for the above process.
WO 2011/037463 discloses an oil recovery system (ORS) for a more effective tar removal from gasified biomass. It uses a first cleaning oil which is based on aromatic hydrocarbons and wherein the mixture of tar and first cleaning oil is separated into a light fraction and a heavy fraction, and the light fraction is reused as first cleaning oil. The second cleaning oil for removing residual tar components is based on aliphatic hydrocarbons.
The use of hydrocarbon oils for removing tars has some disadvantages, such as a limited stability at high temperatures and in the presence of water and oxidative agents, resulting in degradation and loss of oil due to the significant volatility of the hydrocarbons. As a result, the scrubbing liquid and equipment are contaminated and the process must be interrupted at regular intervals for exchange of scrubbing liquid and cleaning of equipment.
U.S. Pat. No. 5,772,734 discloses the use of a wide variety of organic scrubbing liquids, including low-viscosity silicone oils, light minerals oils and glycol ether especially triethylene glycol dibutyl ether for removing organic compounds such as chlorinated hydrocarbons or aromatic hydrocarbons (such as toluene) from industrial gas streams.
It was found that the problems associated with prior art processes can be effectively solved by using a scrubbing oil based on a polysiloxane.